Retired night shift workers exhibit poorer neurocognitive function compared to retired day workers.

Study objectives: Shift work is associated with compromised cognitive function, and with chronic exposure, may place shift workers at elevated risk for dementia. However, evidence of cognitive impairment among former night shift workers is mixed, possibly due to inconsistencies regarding retirement status, work history classification, and cognitive assessments. To address these limitations, this study compared neurocognitive function between retired night shift workers and retired day workers using a well-characterized sample and a rigorous neurocognitive test battery.

Methods: Participants (N = 61; mean age: 67.9 ± 4.7 years; 61% females; 13% non-white) were 31 retired day workers and 30 retired night shift workers equated on age, sex, race/ethnicity, premorbid IQ, years retired, and diary-assessed habitual sleep characteristics. Participants completed a neurocognitive battery assessing six cognitive domains (language, visuospatial ability, attention, immediate and delayed memory, executive function) and self-reported cognitive function. Linear regression models compared groups on individual cognitive domains, adjusting for age, sex, race/ethnicity, education level, and habitual sleep quality.

Results: Retired night shift workers scored lower than retired day workers on attention (B = -0.38, 95% CI [-0.75, -0.02], p = .040) and executive function (B = -0.55, 95% CI [-0.92, -0.17], p = .005). In post hoc analyses, attention and executive function were unrelated to diary-assessed habitual sleep characteristics (disruption, timing, and irregularity) in retired night shift workers.

Conclusions: The observed cognitive weaknesses in retired night shift workers may suggest increased risk for future dementia. Retired night shift workers should be followed to determine whether observed weaknesses progress.